Short answers, pulled from the story.
Martial law was officially declared on the 13th of December 1981 at precisely 00:00. The Polish Council of State approved nationwide martial law shortly before midnight on the 12th of December 1981.
General Wojciech Jaruzelski ordered the Polish General Staff to update plans for nationwide martial law on the 22nd of October 1980. He assumed office as first secretary and later founded the Military Council of National Salvation with high-ranking generals.
Miners at the Wujek Coal Mine in Katowice began striking against the declaration of martial law by General Jaruzelski three days after restrictions were imposed. ZOMO squads and army troops fired at protesters using a shoot-to-kill technique, resulting in eight deaths and twenty-one injuries.
The United States imposed economic sanctions against Poland after the Wujek Coal Mine incident on the 23rd of December 1981. American President Ronald Reagan declared the first anniversary of martial law introduction as Day of Solidarity with Poland on the 30th of January 1982.
Martial law was imposed in clear violation of the country's constitution according to a parliamentary commission established after the fall of Communism in 1989. The Sejm declared the 1981 imposition of martial law to be unlawful and unconstitutional in 1992 because the Sejm had been in session when it was instituted.